Lightly toast the nuts in a medium skillet on medium heat for about 5 minutes.

Once the nuts have cooled, put them in a food processor and pulse a few times, until the nuts are crushed into very small pieces. If you don't have a food processor, put the nuts in a quart-size sealable freezer bag and use a meat mallet or rolling pin crush the nuts into very small bits. Set aside.

Mix the butter and 3/4 cup powdered sugar in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed until the smooth mixture sticks to the side of the bowl. Add the vanilla and beat for 30 seconds to combine.

Add the flour and salt. Mix on low speed until the dry ingredients begin to incorporate, then return to medium speed until a stiff dough is formed.

Mix the crushed nuts in with the dough. Stir on low speed to combine.

Scrape the dough from the bowl into a ball and wrap in plastic wrap. Refrigerate for at least 1 hour, preferably overnight. The dough must be firm and thoroughly cold for best results.

Form small balls of no more than 1 tbsp of dough. Place the balls on the baking mat, spaced evenly.

Bake for 17 to 19 minutes, or until the cookies start to brown slightly on the bottom. There should be very little color on the tops. Allow the cookies to cool to "warm", then roll them in the remaining powdered sugar.

Cookies can be stored in an air tight container on the counter for up to a week.